Spina bifida is a relatively common birth defect
that occurs in 1 to 2 of every 1,000 babies born in the United States.
"Spina bifida" literally means "split spine"; it is caused by failure of
the spinal cord to develop properly.

The nervous system develops from embryonic tissue called the ectoderm. The
first sign of the developing nervous system is the neural plate which can
be seen at about the 16th day of development. Over the next few days, a
"trench" is formed in the neural plate - this creates a neural groove. By
the 21st day of development, a neural tube is formed when the edges of the
neural groove meet. The rostral (front) part of the neural tubes goes on
to develop into the brain and the rest of the neural tube develops into
the spinal cord. Spina bifida occurs when the neural tube is not formed
properly; the bones of spinal column (the vertebrae) and muscle fail
surround the spinal cord properly. No one knows exactly what causes spina
bifida, but it is thought that both environmental and genetic factors play
a role.

Development of
the Nervous System

Skull andVertebrae

Failure of the neural tube to develop properly may result in
three different conditions that lead to spina bifida:

spina bifida occulta - the mildest form of spina bifida
in which one or more vertebrae are malformed. These vertebrae are covered
by a layer of skin.

a meningocele - occurs when the meninges extend out of an opening in the vertebrae.

a myelomeningocele - the most severe form of
spina bifida in which the spinal cord and the meninges extend out of an
opening in the vertebrae.

In both a meningocele and a myelomeningocele, a small sac that bulges out
of the baby's back can be seen. Babies born with spina bifida may have
nerve damage that can cause paralysis, bladder and bowel problems, and
limb and spine disorders. Leakage of cerebrospinal fluid from the defect
in the spinal cord may cause the brain to bulge out near the cerebellum.
This may block the flow of cerebrospinal fluid and result in
hydrocephalus.

Babies with spina bifida usually have surgery within the first 24 to 48
hours after birth to repair the spinal cord and brain. Sometimes a shunt
is placed in the baby's head to drain away excess fluid and reduce
pressure on the brain caused by hydrocephalus.

Two papers in the Journal of the American Medical
Association describe the results of attempts to fix the defect in the
spinal cord while babies are still developing within their mothers.
During this procedure, surgeons open the womb of the mother and repair
the damaged back of the baby. Doctors at Children's Hospital in
Philadelphia and at Vanderbilt University Medical Center report that the
need for shunts was decreased and the incidence of hindbrain swelling was
reduced after this procedure.

Fetal surgery for spina bifida still has risks. Fetal surgery appears to
increase the chance of premature birth and mothers may develop
complications such as rupturing of the uterus and bowel obstruction.
Because this type of fetal surgery is not performed very often, some
physicians view the procedure as experimental. Nevertheless, these
pioneering studies may lead to other ways that improve the quality of life
for babies born with spina bifida.

References and further information:

Bruner, J.P. et al., Fetal
Surgery for Myelomeningocele and the and the Incidence of
Shunt-Dependent Hydrocephalus, Journal
of the American Medical Association 282:1819-1825, 1999.